A general technique of red staining borosilicate glasses wherein copper ions obtained from copper halide vapors are substituted for alkali metal ions in the glass and thereafter converted to metallic copper imparting a red color has been known for many years. The historical treatment of this development activity appears in Chapter XXVII of the textbook entitled "COLOURED GLASSES" by W. A. Weyl, Society of Glass Technology, 1951, which includes reference to the process of reacting copper halide vapors with the glass surface for ion replacement of the alkali ions by copper ions. All of said references utilize a double firing technique for the desired color production, however, and which can further include still additional firing steps to produce the proper color brightness or intensity.
It would be beneficial if such general process of staining borosilicate glass articles to produce red coloration could be improved to eliminate multiple firing steps. It would also be desirable from a cost standpoint to eliminate the need for silver ions in the staining composition which serve as nucleating agent for copper staining a borosilicate glass in the conventional manner. Said conventional staining process provides only yellow coloration to the glass after initial firing in air which produces migration of copper and silver ions from the staining composition to exchange for alkali metal ions in the glass. A second heating step conducted under reducing atmosphere conditions is required by said conventional staining process to reduce the coloring ions to atoms and thereby produce darker coloration in the glass. The coating originally applied to the glass article to produce said stain is also generally removed before the second heating step in order to provide better results.
It is a principle object of the present invention, therefore, to provide an improved method for copper red staining borosilicate glass which utilizes but a single heating step in achieving the desired red color. Another important object of the present invention is to provide an improved method for copper red staining of borosilicate glass which further requires but a single cleaning step to remove residual process materials from the treated glassware.